1. Field of the Invention
The present invention relates to a solid-state imaging device, a signal processing device and a signal processing method for the solid-state imaging device, and an imaging apparatus.
2. Description of the Related Art
In recent years, in a CCD (Charge Coupled Device) image sensor and an amplification-type image sensor known as solid-state imaging elements suitable for applications such as a video camera and a digital still camera, a pixel size is further reduced through an increase in the number of pixels and a reduction in an image size at high sensitivity.
On the other hand, in general, solid-state imaging elements such as a CCD image sensor and a CMOS (Complementary Metal Oxide Semiconductor) image sensor tend to be used under various environments such as the indoors and the outdoors and in the daytime and at night. When the solid-state imaging elements are used under such environments, it is necessary to adjust an exposure period by, for example, controlling charge accumulation time in a photoelectric conversion element and set sensitivity to an optimum value according to a change in external light and the like.
As a method of expanding a dynamic range of the CMOS image sensor, there have been proposed, for example, a method of combining plural frames photographed in plural exposure periods as shown in FIGS. 19A and 19B (see, for example, JP-A-2004-363666 (hereinafter referred to as Patent Document 1)) and a method of expanding a dynamic range by applying different exposure periods to respective rows of a pixel array as shown in FIGS. 20A and 20B (see, for example, “High Dynamic Range Imaging: Spatially Varying Pixel Exposures” IEEE Conference on Computer Vision and Pattern Recognition 2000 (hereinafter referred to as Non-Patent Document 1)).
In the following explanation, the former method is referred to as a wide dynamic range method 1 and the latter method is referred to as a wide dynamic range method 2. In the wide dynamic range methods 1 and 2, plural images with different sensitivities are acquired as a first video signal, a second video signal, and the like. As an example, the acquired plural video signals are added up and combined to obtain an image with a wide dynamic range.
In FIGS. 19A and 19B and FIGS. 20A and 20B, the abscissa PO indicates the intensity of incident light and the ordinate YL indicates an output of a sensor (a light receiving unit). FS represents a saturation level of the sensor. With one video signal, it is difficult to obtain an output signal with a saturation level equal to or higher than FS.